The production of materials based on polyurethane and other polymer systems derived from organic polyisocyanates is well established. Depending upon the formulations used in their manufacture, the products can vary in texture from the rubbery, elastomeric thermoplastic polyurethanes to the soft flexible foams used as cushioning materials to the rigid foams used as insulating or structural materials.
Flexible polyurethane foams are produced by reacting a polyol with a polyisocyanate in the presence of a foam-forming agent. Flexible polyurethane foams are used to make resilient structural materials such as cushioning or padding materials in the furniture and automotive industries. It is known to incorporate fire-retardant additives into such foam materials. However, care has to be taken so that adequate fire retardancy can be achieved without adversely affecting the desired physical properties of such foam materials.
Rigid polyurethane foams are produced by reacting a polyol with a polyisocyanate in the presence of blowing agents, surfactants and catalysts. Rigid polyurethane foams are typically used to in insulation applications, including insulation panels and light-weight laminated structural applications.
Blends of alkylated triphenyl phosphate with pentabromodiphenyl oxide have been used as flame retardants for flexible polyurethane foams and as flame retardant plasticizers in polyvinyl chloride (PVC) products. Due to environmental concerns, the use of pentabromodiphenyl oxide is being phased out of use, and alternative substitutes are being sought.
Dialkyltetrahalophthalate esters have been extensively researched. Di(2-ethylhexyl)tetrabromophthalate (DEHTBT) is a well known, commercially available flame retardant that is recommended for use in PVC, thermoplastic elastomers, and adhesives/coatings and is disclosed in International Publication No. WO 89/03854 to Pennwalt Corp.
The broad class of organophosphorus compounds, optionally halogenated, have long been used to reduce the flammability of substrates containing these materials. In particular, trialkyl phosphates, mixed alkylaryl phosphates, alkylated triaryl phosphates, and halohydrocarbyl phosphates are recognized flame retardant additives for a number of applications, including PVC and flexible polyurethane foams. Mixtures of different types of flame retardants are also known. Blends of alkyldiphenyl phosphate with DEHTBT are disclosed, and blends of alkylated triaryl phosphates with DEHTBT for use in PVC are suggested in U.S. Pat. No. 4,892,683 to Naseem and U.S. Pat. No. 5,036,121 to Coaker et al. Alkylated triaryl phosphate blends with DEHTBT as flame retardant hydraulic fluids are disclosed in U.S. Pat. No. 5,328,627 to Bohen et al.
The use of organophosphorus flame retardants, combined with halogenated flame retardants, in polyether flexible urethane foams are disclosed in U.S. Pat. No. 4,880,844 to Fesman. Similarly, U.S. Pat. No. 4,407,981 to Aaronson discusses the use of separate sources of organophosphorus and organohalogen flame retardants in polyurethanes and discloses the classes of “esters and imides of tetrabromophthalic anhydride” in a broad list of suitable organohalogen substances.
European Patent Application Publication No. 0 005 903 to Imperial Chemical Industries Ltd. discloses the use of dialkyl tetrabromophthalates with triaryl phosphates in rigid polyurea foams, with no suggestion of the applicability to flexible polyurethane foams.
U.S. Pat. No. 5,728,760 to Rose et al. describes a family of brominated benzoate esters that are especially suited to use in flexible polyurethane foams. A means of producing the esters is via decarboxylation of half esters made from tetrabromophthalate anhydride.